Hitherto, mobile communication systems have been arranged so that a communication provider offering services determines a cell coverage, that is, a service area of each base station (hereinafter simply referred to as a “base station”) for communicating with mobile terminals, and sets a radio parameter for the base station to obtain the cell coverage. The radio parameter is, for example, data of power transmitted from the base station to each cell, the height, the pattern, and the tilt angle of an antenna, etc. When the operation of the mobile communication system is started after setting the above-described specified radio parameter, it often becomes difficult to obtain originally planned cell coverages later due to a change in the operation conditions of the mobile communication system and a change in the radio environment (e.g., a change in a path loss occurring due to a newly constructed building). Therefore, the communication provider measures the cell coverage of the base station by measuring the reception power of a radio wave transmitted from the base station with a radio wave-measurement apparatus or the like to maintain the quality of communication services that are offered to a user of the mobile communication system. A cell coverage obtained as a result of the measurement (a measured cell coverage) is compared to an originally planned target cell coverage (a target cell coverage), and the above-described radio parameter is changed at regular intervals or at irregular intervals as appropriate.
On the other hand, a base station configured to automatically set the antenna pattern has been disclosed as a method of dynamically adjusting the above-described radio parameter (e.g., see Laid-open Patent Publication No. 2008-48107). The base station allows for determining the status of radio resources that are used thereby based on the statistic of usage of the radio resources, the usage being observed thereby, and specifying the antenna pattern thereof based on the determined radio resource-use status. The radio resource usage is determined based on the uplink interference amount and/or the total transmission power observed in the cell of the base station.
However, it takes much time and manpower to measure the reception power by using the radio wave-measurement apparatus at regular intervals or at the irregular intervals to obtain the measured cell coverage. Therefore, it is difficult to update the above-described radio parameter at short time intervals even though the radio environment of the mobile communication system may change at all times. Consequently, the above-described radio parameter is not updated at appropriate time, so that the measured cell coverage may diverge from the target cell coverage, that is, many underserved areas may occur.
On the other hand, according to the above-described known method for dynamically adjusting the radio parameter, the base station only considers the amount of radio resources that are used in the cell thereof and does not consider the status of radio links that are established between mobile terminals existing in the cell thereof and other cells. Therefore, the above-described known method may not be appropriate for optimizing the entire communication environment of an area including a plurality of base stations. For example, even though a given base station sets a radio parameter which is appropriate in terms of the radio resource usage, the set radio parameter may not be appropriate for other base stations that are adjacent to the given base station.